Perforating wells



April 29, 1958 c. E. REISTLE, JR 2,832,415

PERFORMING WELLS Filed oct. 12, 1955 IN VEN TOR.

PERFORATHNG WELLS Carl E. Reistle, Jr., Houston, Tex., assignor, bymesne assignments, to Esso Research and Engineering Company, Elizabeth,N. J., a corporation of Delaware Application October 12, 1955, SerialNo. 540,067

6 Claims. (Cl. 166-22) The present invention is directed to a method forcompleting wells. More particularly, the present invention is directedto a method for perforating wells. In its more specific aspects, theinvention has to do with forming clean perforations in subsurface earthformations.

The present invention may be briey described as a method for formingclean perforations in a well bore penetrating a subsurface earthinterval, zone, or stratum from which desirable earth uids, such as oiland/or gas, water,

and the like may be produced. In the present invention, a body of asuspension of an acid-soluble material is arranged in the well bore,which may have a casing arranged therein, adjacent the earth intervalfrom which the desired fluid is to be produced. The well bore and/orcasing, if one is employed, is then perforated by operating aperforator, such as a bullet or shaped charge gun perforator, whereby anacid soluble iilter plug is formed in the resulting perforations.Thereafter, the lilter plug is treated with an acid whereby the filterplug is dissolved and the desirable earth iiuid is then produced throughthe treated, clean perforations.

The acid-soluble material is preferably employed as an aqueoussuspension and may include materials, such as colloidal clay, whichcontains montmorillonites, such as calcium and sodium montmorillonites,bentonite, and the like. The acid-soluble material includes a material,such asv powdered or finely divided calcium carbonate which may be usedwith the bentonite in a ratio of bentonite to calcium carbonate in arange from 1:5 to about 1:10. The suspension of bentonite and calciumcarbonate may suitably contain a small amount of alkaline material, suchas an alkali metal hydroxide, for example, sodium hydroxide and thelike. Other acid-soluble materials may be used and for purposes ofexample finely divided or powdered acid-soluble materials, such as lime,magnesium hydroxide, zinc oxide, stannous oxide, calcium sulfide,ferrous hydroxide, ferrie hydroxide, barium sulfide, ferrous lactate,magnesium lactate, calcium lactate, and the like, may be formed inpreferably an aqueous suspension and employed in the well bore.Preferably, calcium carbonate is employed.

In the completion of oil and/ or gas wells by gun perforating, the wellYfluids under considerable hydroy static head will enter theperforations formed by the perforator to form lter cakes in theperforatons or holes. These well uids normally are made up of a liquidcarrier bo'dy plus a solid material andare employed as drilling fluidsin drilling the well. The density of the drilling tiuid is such as toprovide -a pressure differential toward the formation in order tomaintain the well under control until well Vcompletion equipment may beinstalled. Filtration 'results from this pressure differential andcauses a hard filter cake of very low permeability to be deposited from'the 'drilling liuid in the perforations. When employing a shaped chargeIgun perforator, solid material from the shaped charge is also includedin the filter cake. These filter cakes or plugs hinder the flow of oilaud/or gas intothe well bore and later may be a barrier to a 2,832,415Patented Apr. 29, 1958 ging of the perforations with the material whichforms a lter cake therein may absolutely nullify the perforationoperation. l

In accordance with the present invention wherein the` well is perforatedin an acid-soluble material to form an acid-soluble lter plug which issubsequently removed by treatment with acid, clean perforations areformed and the wells are producible without hindrance from the filterplugs.

The acid-soluble filter plugs may suitably be treated with a mineralacid preferably hydrochloric acid which may suitably be inhibited toprevent corrosion of exposed ferrous metal surfaces in the wellequipment. Other mineral acids, such as sulfuric acid and nitric acid,may be used and the organic acids may also be employed. Whatever acidsmay be used it may be desirable to inhibit same to mitigate attack bythe acid on theferrous metal and other metallic equipment.

The present invention will be further illustrated by reference to thedrawing in which Figs. la to le are step'- wise illustrations of thepractice of the present invention.

Referring now to the drawing in which identical numerals will beemployed to designate identical parts, numeral 11 designates a well boredrilled from the earths surface to penetrate a plurality of earthformations A, B and C. A and C are productive earth intervals or zones,strata and the like which may contain oil and/or gas while interval Bwhich separates intervals A and C may be non-productive.

Arranged in the well bore 11 is a casing 12 which is cemented in placewith a primary cement job 13. Run into and preferably permanently set inthe well is a tubing 14 which may be arranged with its lower open end 15above the interval C. With the tubing permanently set in the well and asshown in Fig. la, if it is desired to recomplete or service the well ata lower interval, a tubular extension member, such as illustrated by thenumeral 16 may be lowered on a wire line, not shown, and landed,anchored or supported in a landing nipple 17 and sealed therein withpacking 18. The tubular extension member 16 then may be used to form apath down to the interval C. The extension member 16 is provided with anopen upper end 19 having a fishing neck 20 for removal of the tubularextension member from the tubingv 14. Fig. la shows the well aftercementing and tubing arranged therein and Fig. 1b shows the tubing 14with an acid-soluble material indicated by the numeral 21 arranged in abody in the well adjacent the hydrocarbon productive interval C.Drilling mud or uid'in the well in Fig. la is removed prior to locatingthe acid-soluble suspension, as shown in Fig. lb. All or part of thedrilling mud is replaced by the suspension. For example, only sufcientsuspension may be used to protect the interval C which is to beperforated. If desired, the body 2l may be deposited in the Well usingthe tubular extension member 16 if per! marient Well completionoperations are employed or if permanent Well completions are not usedthe tubing 14 would be lowered as indicated by the dotted lines and thenagents may be used.

assaggio InfI-igtle a-tubinggun-perforator- 22V isloweredu on a*- wireline 23 through the tubing 14 adjacent the interval C. This tubing gunperforator 22 may be a bullet or shapedlchargeiperforator whichfi'stheniiredlto f'orm the perforationsA 2li-penetrating the casinglZ,cement 1'3 and;

th'efformationor intervaly C. These perforations, by virtuefof theacid-soluble suspension 21, become 'plugged'with lter plugs indicated bynumeral 25 of an acidsoluble' material.V After firing of thev gunperforator 22 andrforrning'the-'perforationsV 24- containing theacid-soluble-filterV plugsy 25, any residual acid-soluble suspension inthe casing 12 may then be removed by manipulating Vthe tubing 14or'byusing the tubular extension member 16, asfshown intFig. la. Thereafter abodyI of acid, such as"26.is-deV positedin the well casing below the'ltubing ldwhich causes;l thedissolutionfof Vthe.y filter plug 2.5"leavingthe perforations'24 in a'clean conditionaud providing anunobstructedpath from the formation C into the well bore.

Thereafter, asshown in'Fig. 1e, the acid is removed orcirculated.fromtlieewellcasing 12- and production is then badi-from `theinterval C through the clean perforations Afterproduction has ceasedfrom interval C or has become uneconomical, the perforations 24 may thenbe' sealed by depositing cement adjacent the interval C to formr plugsin the perforations 24. After perforations 24 have been sealed off withcement, then the interval A or other productive intervals,.as may bedesired, may be gun perforated in an acid-soluble.. suspension to formyacid-soluble lter plugs which may be removed by treatingthe acidsolubleiilter plugs with-an acid as'hasbeen described. Whererecompletionoperations are performed` andy an.interval such. as C issealed, .it may be desirable to protect the sealed intervalagainstattack byfacid since the sealed perforations may become unplugged vifcon-- tactedwith acid. In those instances, a body of oil, drillingl mudand the like, may be arranged adjacent the sealed interval at leastduring the time the perforated inteival isfbeing vtreated with acid'todissolve the acid-soluble plu-g.

InV order to illustrate the invention further, several compositions wereprepared and subjected to various tests.l Thereafter vilter cakesprepared from the composition were treated with hydrochloric acid todetermine the solubility of the filter cakc in the acid. The resultsofth'eseftests are shown in the following table:

yhad through clean perforations.

with the drawing, it will be seen that wells may bereadily completed bygunperforating and the like without plugging the wells. and allowingproduction to. be

The' nature and objects of' thepresent inventionhaving been completelydescribed and illustrated, what I wish toclaim'as new and useful and tosecure by Letters Patent is:

1. A method for forming clean perforations in a cased Y wellbore,penetratingr a= subsurface earth interval which comprises locatinga 'body ofasuspension ofanA acidAl soluble materialinvr said wellfboreadjacentV saidfinteival',

said'acidesolublematerial containing-a-component selected from the groupconsisting of calciumV carbonate; 4sodiumliydroxid'eg-lime, magnesiumhydroxide, zinc oxide, stannousbxide, calcium sulde, ferrous'hydroxide,ferrie hy droxidbarium sulfide, ferrouslactate, magnesium lactateandYcalcium lactate, gunfperforatingsaidintervalin said body whereby an acidsolubleiilte'r plug is vformed iny the' resulting iperforationsin'saidcasing and said interval, and

then treatingisaidiilter plug with-an acid, selected fromthe-'groiipconsisting ofhydrochloric-acid, sulfurieacid'" andnitricfacidu/hereby said lter p lug isdissolved:

2l' Afmethodl in Yaccordance with claim 1 inI which'f the'suspensionf is,an4` aqueous suspension of bentonite and: calcium carbonate and theacid is hydrochloric acid.

3i Anietliod ih accordance with claim 2 in whichthe bentonite andcalciumcarbonate are employed in a ratio in the'range-froin-about" lf: 5 toabout' 1 10.

4. A method for forming clean perforations inta'well'f bore penetratinga productive subsurface earth interval having-a wellcasingfarrangedtherein which comprises locating a bodyof "zt-.suspension of an acidsoluble ma# terial in' said wellcasing adjacent'said interval, saidacid-soluble m'ateri'al'containingl a component selectedy from theegroupconsistingfof calciumL carbonate, sodium:v

Tab lew Initial Gel- Viscoslty API Filf Strength, gat '600' tration',Observations .of Composition Stability Grams R.YP. M. ce. m30 FilterCake Stormei"v Stormer, Min.

cps.

10 lbs. bentonite per bbl. water "Ihln,v irni'. cake;l lbs` calciumcarbonate per bbl; water }Ngl.mg 2 9 23 readllyvsoluble. Trace sodiumhydroxide 20 lbs. starch per bbl. water... I A Y y l5 lbs. bentonite perbbl. water S'etisled'ratbe'rv 2 37' l13 Do. 0.6'lb; sodium hydroxide perbbl. water... badly. Y 50 lbs. calcium carbonate per bbl. waterg It willbe seen from these data that a composition con` taining bentonite andcalcium carbonate in the ratio of 1:5

forms a thin, firm iilter cake which was readily soluble in acid. fromwhich settling was not obtained. Whereas, f

one containing starch, bentonite and calcium' carbonate where the ratioof bentonite to ycalcium carbonate was 1:10

rather than 1:5, as in the iirst composition, resulted in a.

It is preferable to employ/an aqueous suspension-ofvacid-solublematerial since suspensions formed in oil-inwater'emulsioris,while settling out slowly, did not" dissolve as readily as those formedfromaqueousisuspenf hydr'oxideliine magnesium hydroxide, zineroxide,stan.- nous oxide," calcium. sulfide, ferrous hydroxide, ferriehydroxide, barium sulfide, ferrous lactate, magnesiurnflactatef and.ca-lcimlactate, inserting a gun perforatorintosaidbody, operatingfsaidperforator to. penetrateA said casingy and'said earthinterval adjacentsaid. casing whereby an acid'soliibleiilterl plug is formed in thelresulting perforations,'-t'rea'tin'gsaid' plugged. perforations with anacid,v

selectedfro'rn the group consisting ofhydrochloric acid, sulfuricV4 acidvand nitric. acid whereby said ilterplugis dissolvediland then producinga: desirable earth-huid" througl saidf treated perforations..

11A' methodlinacordanc with claim. 4- mwhicli.

suspensihis an aqueous alkaline suspension of bentonite and' calciumAcarbonate andthe acid.'ishydrochloric:

6. A method in accordance with claim 5 in which the n 5 6 bentonite andcalcium carbonate `are employed in a ratio 2,193,807 Dieterich Mar. 19,1940 in the range from about 1:5 to about 1:10. 2,591,807 Greene APL 8,1952 References Cited in the le of this patent 2,693,856 Allen NOV. 9,1954 UNITED STATES PATENTS 2,699,213 Cardwell et al. Jail. 11, 1955 52,045,899 Davis June 30l 1936 2,718,264 Allen et al. Sept. 20, 1955

1. A METHOD FOR FORMING CLEAN PERFORATIONS IN A CASED WELL BOREPENETRATING A SUBSURFACE EARTH INTERVAL WHICH